This obviously creates a paradox, as you can't pay taxes on revenue generated by "nothing". I don't know which European country you're from, but I'm Norwegian.

Our tax authorities didn't recognize BTC as being VAT (value added tax) exempt until about three years ago. For the time being you're in a legal limbo, and at the bare minimum I would advice you to report any BTC holdings on your tax returns.

However, I wouldn't start paying taxes on an unrealized gain (although I don't know what your intention is with the investment)..As soon as you exchange that money into fiat currency, the snowball starts moving though.

Best of luck regardless.